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Leak-Tightness

All Tight? – Technical Leak-Tightness of Pressure Reactors

| Author / Editor: Dr. Kerstin Dreblow, Matthias Hörbe* / Wolfgang Ernhofer

General reactor design
General reactor design (Picture: Berghof)

The system leak-tightness is a basic prerequisite for a safe reaction in chemical synthesis under pressure. The design is as critical as the selection of suitable components in this context.

Pressure reactors, i.e. closed systems, operated under high or low pressure, are an indispensable asset in modern synthetic chemistry and material science. These reactors were already used in geology during the 18th century, to simulate rock formation processes in the earth's crust. These closed systems enable highly increased operating temperatures and pressures, which speed up the reaction kinetics significantly, thus enable a tailored synthesis. Modern advanced pressure reactors must not only meet the applicable safety regulations but also enable extensive flexibility and modularity, e.g. with regards to accessories, in order to allow for a variety of synthesis processes.

Technical regulations for pressure reactors

Due to the involvement of corrosive media and gases, reactors must be easy to operate, technical safe and leak-tight during the overall synthesis process. The technical regulations must be observed in this regard. Pressure reactors are designed, manufactured and tested according to the European Pressure Equipment Directive 97/23/EC and the German AD2000 regulation.

The reactors are tested hydrostatically at the prescribed overpressure and are also subjected to leak tests, which must be passed successfully, to obtain a factory certificate. In addition, high-pressure reactors must be classified as “equipment requiring inspection”. Reactors with volume of up to 1,000 ml and an operating pressure of 200 bar are not subject to labelling obligation and may not be identified with a CE label.

Leak-tightness of connections and fittings

The complexity of modern synthesis requires a high configuration variety of the overall system with regards to connections and fittings. Materials in varying physical conditions must be reliable to this end and tested or introduced into the reactor without leakage. The connections and fittings used must therefore be "permanently technically leak-tight". This term is defined in more detail in the TRBS 2141 (technical reliability regulation) and stipulates that equipment components are "permanently technically leak-tight" if:

  • their technical design ensures a continuous technical leak-tightness; or
  • their technical leak-tightness is permanently ensured through maintenance and supervision, e. g. with foaming agents, leak detection systems or leak indication systems.
  • In addition, the TRGS 500 (technical hazardous substances regulation) defines, which connections are suitable for a use in a closed system, like e.g. a pressure reactor. The following static seals are considered as technically leak-tight equipment components:
  • Flanges with a smooth raised face and suitable sealings. Leak-tightness to be ensured through supervision and servicing.
  • Compression fittings <DN 32 without limitation
  • NPT threads < DN 50 and T < 100 °C without limitation. Leak-tightness to be ensured through supervision and servicing.

Sealing concept for pressure reactors

The leak-tightness of the reactor system is of special importance for material testing applications, in which a test body is exposed to high temperatures and pressures over an extended time period. The design must ensure the system's pressure resistance and leak-tightness and also prevent leakage during operation and maintenance activities.

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